EP1396852A2

EP1396852A2 - Optical pickup having a shielding magnet

Info

Publication number: EP1396852A2
Application number: EP03254074A
Authority: EP
Inventors: Myung-sik 945-711 Lotte Apt. Kwon; Jung-gug 544-202 Ssangyong Apt. Pae
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2002-09-02
Filing date: 2003-06-26
Publication date: 2004-03-10
Anticipated expiration: 2023-06-26
Also published as: DE60313714D1; TWI254933B; CN1480928A; KR20040021063A; KR100472477B1; DE60313714T2; TW200404280A; CN1248204C; US20040107427A1; JP2004095161A; EP1396852B1; US7340756B2; EP1396852A3

Abstract

An optical pickup actuator, an optical pickup employing the optical pickup actuator, and an optical disc drive apparatus employing the optical pickup are provided. The optical pickup actuator includes a blade (37) on which an objective lens (39) for condensing light onto an optical disc is mounted, and in which coils (32,36) are wound, and a base (35) which includes a plurality of driving magnets (31a,31b), which interact with current flowing through the coils (32,36), to generate force that drives the blade (37) in a predetermined direction and a shielding magnet (40), which is arranged opposite to and has the same polarity as at least one of the driving magnets (31a,31b), to block leakage magnetic flux from the driving magnets (31a,31b).

Description

The present invention relates to an optical pickup actuator, an optical pickup, and an optical disc drive apparatus, and more particularly, to an optical pickup actuator for blocking leakage magnetic flux, an optical pickup employing the actuator, and an optical disc drive apparatus employing the pickup.
An optical pickup actuator is used in an optical recording apparatus for recording and reproducing data on an optical disc. Recently, as optical recording apparatuses become smaller and their compact disc access time becomes shorter, an optical pickup actuator having a lower height and a faster follow-up speed is required. Also, the optical pickup actuator should be designed for existing optical discs such as CDs and DVDs.
Such an optical pickup actuator should have the same or wider operation range as existing optical pickup actuators to satisfy the aforementioned requirement. Leakage magnetic flux generated in a magnet installed in an optical pickup actuator interacts with current to produce a nonuniform thrust force in the optical pickup actuator. This nonuniform thrust force causes negative resonance in the optical pickup actuator which increases as the access time of the optical pickup actuator decreases. Here, negative resonance means an unstable operation of an optical disc caused by resonance at natural frequencies of the optical disc and the optical pickup actuator.
Figure 1 is an exploded perspective view of a conventional asymmetric optical pickup actuator. Referring to Figure 1, the conventional optical pickup actuator includes first and second magnets 11a and 11b, yokes 13a and 13b in which the first and second magnets 11a and 11b are fixed, a base 15 on which the yokes 13a and 13b are installed, a focusing coil 12 and tracking coils 16 which interact with the first and second magnets 11a and 11b and generate electromagnetic force, a blade 17 provided so that the focusing coil 12 and the tracking coils 16 interact with the first and second magnets 11a and 11b, an objective lens 19 seated on the blade 17, and a suspension 18 which supports the blade 17.
Figure 2 shows magnetic field lines around the first and second magnets 11a and 11b and the focusing coil 12 of the optical pickup actuator shown in Figure 1.
Focusing and tracking operations of an optical pickup are performed by an electromagnetic force F resulting from interaction of the first and second magnets 11a and 11b installed in the yokes 13a and 13b with the focusing coil 12 and the tracking coils 16 installed in the blade 17. The electromagnetic force is given by Equation 1 below. F = IL × B
Here, F is the electromagnetic force vector measured in Newtons [N], I is the vector current measured in Amperes [A], L is the length of a section of the coil affected by the magnetic field measured in meters [m], and B is a magnetic field vector in the region of the section of coil measured in Tesla [T].
The optical pickup actuator performs a focusing operation in order to read or record data on an optical disc and operates within an operational range so as to follow-up the optical disc when the optical disc is shaken. During the follow-up operation, the optical pickup actuator moves upward and downward with respect to a plane of the base 15. The electromagnetic force that acts on the focusing coil 12 and the blade 17 is generated by a magnetic field B and current I due to current flowing through a coil placed between the first and second magnets 11a and 11b, as shown in Equation 1. In order to drive the optical pickup actuator in a focusing direction, it is preferable that magnetic flux only exists between the first and second magnets 11a and 11b. However, in reality, magnetic flux also leaks behind the second magnet 11b, thereby causing negative resonance.
Such leakage magnetic flux generated from an N pole of the second magnet 11b shown in Figure 2 interacts with current flowing through the section of the focusing coil 12 placed behind the second magnet 11b. Due to this leakage magnetic flux, a nonuniform electromagnetic force is generated in the focusing direction, thereby providing a cause of negative resonance in the optical pickup actuator. Due to the negative resonance in the optical pickup actuator, the optical pickup operates unstably, and the overall performance of an optical disc drive apparatus is lowered.
Embodiments of the present invention aim to provide an optical pickup actuator which blocks leakage magnetic flux such that an unstable operational factor such as negative resonance occurring due to a nonuniform thrust force is removed, an optical pickup employing the optical pickup actuator, and an optical disc drive apparatus employing the optical pickup.
According to the present invention there is provided an apparatus and method as set forth in the appended claims. Preferred features of the invention will be apparent from the dependent claims, and the description which follows.
According to an aspect of the present invention, there is provided an optical pickup actuator. The optical pickup actuator includes a blade on which an objective lens for condensing light onto an optical disc is mounted, and in which coils are wound, and a base which includes a plurality of driving magnets, which interact with current flowing through the coils, to generate force that drives the blade in a predetermined direction and a shielding magnet, which is arranged opposite to and has the same polarity as at least one of the driving magnets, to block leakage magnetic flux from the driving magnets.
According to another aspect of the present invention, there is provided an optical pickup. The optical pickup includes an optical pickup actuator which comprises a blade on which an objective lens for condensing light onto an optical disc is mounted, and in which coils are wound, and a base which includes a plurality of driving magnets, which interact with current flowing through the coils, to generate force that drives the blade in a predetermined direction and a shielding magnet, which is arranged opposite to and has the same polarity as at least one of the driving magnets, to block leakage magnetic flux from the driving magnets, and an optical system which includes the objective lens and a light source for radiating light through the objective lens.
According to another aspect of the present invention, there is provided an optical disc drive apparatus. The optical disc drive apparatus includes an optical pickup which comprises an optical pickup actuator including a blade on which an objective lens for condensing light onto an optical disc is mounted, and in which coils are wound and a base which includes a plurality of driving magnets, which interact with current flowing through the coils, to generate force that drives the blade in a predetermined direction and a shielding magnet, which is arranged opposite to and has the same polarity as at least one of the driving magnets, to block leakage magnetic flux from the driving magnets, and a slider at one end of which the optical pickup actuator is mounted at one end and which forms an air bearing with the optical disc to provide lift, an optical disc rotating unit which rotates the optical disc at a predetermined speed, a driving unit which drives the optical pickup and the optical disc rotating unit, and a control unit which controls focusing and tracking servos of the optical pickup.
The base comprises a holder to which the shielding magnet is attached, and a plurality of yokes to which the plurality of driving magnets are fixed.
The blade comprises a plurality of guide holes into which the plurality of driving magnets are inserted.
The coils comprise a focusing coil wound to generate an electromagnetic force in a focusing direction and a tracking coil wound to generate an electromagnetic force in a tracking direction.
The base comprises a suspension, one end of which is coupled with the holder and the other end of which is connected to the blade, to support the blade to be movable.
For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:
Figure 1 is an exploded perspective view of a conventional optical pickup actuator;
Figure 2 shows magnetic field lines around magnets and a coil installed in the conventional optical pickup actuator;
Figure 3 is an exploded perspective view of an embodiment of an optical pickup actuator according to the present invention;
Figure 4 is a plan view of the optical pickup actuator shown in Figure 3;
Figure 5 shows the distribution of magnetic field lines around magnets installed in the optical pickup actuator according to an embodiment of the present invention; and
Figure 6 schematically shows an embodiment of an optical disc drive apparatus according to the present invention.
Hereinafter, preferred embodiments of an optical pickup actuator, an optical pickup, and an optical disc drive apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
Figure 3 is an exploded perspective view of an embodiment of an optical pickup actuator according to the present invention, and Figure 4 is a plan view of the optical pickup actuator shown in Figure 3.
Referring to Figures 3 and 4, the optical pickup actuator comprises a base 35 and a blade 37. A holder 34 is formed at one side of the base 35, and a magnetic driving part 30 is formed at the other side of the base 35 and in the holder 34. The blade 37 is coupled with the base 35 and an objective lens 39 is seated on a side of the blade 37 opposite to the holder 34. The base comprises a suspension, one end of which is coupled with the holder and the other end of which is connected to the blade, to support the blade to be movable.
The magnetic driving part 30 includes first and second yokes 33a and 33b fixed to the base 35, first and second magnets 31a and 31b attached to the first and second yokes 33a and 33b, and a shielding magnet 40 separately installed at the holder 34 to shield magnetic flux which leaks from the second magnet 31b.
First and second guide holes 41 and 43 are formed in the blade 37, a focusing coil 32 is wound around the second guide hole 43, and tracking coils 36 are disposed at one side of the focusing coil 32.
Referring to Figure 4, the focusing coil 32 includes an effective section 32a, which crosses the middle range of the first and second magnets 31a and 31b and an ineffective section 32b, which crosses a back side of the second magnet 31b. Current flowing through the effective section 32a interacts with the magnetic field formed between the first and second magnets 31a and 31b to result in a force in a focusing direction according to Equation 1. However, current flowing through the ineffective section 32b interacts with only minor magnetic flux which leaks in the second magnet 31b to cause a nonuniform thrust force. That is, the current flowing through the ineffective section 32b, which is not used to drive the optical pickup actuator in the focusing direction, causes unstable negative resonance in the optical pickup actuator.
Thus, the technical feature of the present invention is that the shielding magnet 40 is attached to the holder 34 opposite to the second magnet 31b so as to shield the ineffective section 32b from leakage magnetic flux. Here, the second magnet 31b and the shielding magnet 40 should have the same polarity.
Figure 5 shows the distribution of magnetic field lines around the first and second magnets 31a and 31b and the shielding magnet 40, according to an embodiment of the present invention. Referring to Figure 5, the first and second magnets 31a and 31b are positioned to each have opposite polarities facing and magnetic field lines go from an N pole of the first magnet 31a to an S pole of the second magnet 31b. On the other hand, the second magnet 31b and the shielding magnet 40 are arranged to each have the same polarity facing and magnetic field lines come from N poles of the second magnet 31b and the shielding magnet 40 and are mutually deflected away from the center of the space between the first and second magnets 31a and 31b, parallel to the ineffective section 32b of the focusing coil 32 (not shown in Figure 5). As is known from Equation 1, when the magnetic field is perpendicular to the current, a maximum force is generated, and when the magnetic field is parallel to the current, no force is generated. Thus, as shown in Figure 5, the magnetic field formed between the second magnet 31b and the shielding magnet 40 does not affect the ineffective section 32b which crosses there.
That is, the optical pickup actuator according to the described embodiment of the present invention further includes the shielding magnet 40 behind the second magnet 31b such that the effect of leakage magnetic flux on the ineffective section 32b of the focusing coil 32 is minimized. The optical pickup actuator according to the embodiment of the present invention is mainly used as a slim and lightweight asymmetric optical pickup actuator for a portable type.
Figure 6 schematically shows an embodiment of an optical disc drive apparatus according to the present invention. Referring to Figure 6, the optical disc drive apparatus includes an optical disc rotating unit (spindle motor 52) which rotates an optical disc D, an optical pickup 50 which is installed to be movable in a radial direction of the disc D and reproduces information recorded on the disc D or records information on the disc D, a driving unit 54 which drives the spindle motor 52 and the optical pickup 50, and a control unit 56 which controls focusing and tracking servos of the optical pickup 50.
The optical pickup 50 includes an objective lens, an optical system having a light source for radiating light through the objective lens, and an actuator on which the objective lens is seated and driven in focusing and tracking directions. The optical pickup 50 further includes a slider, at one end of which the actuator is mounted and which forms an air bearing with the optical disc D to provide lift. Reference numerals 53 and 51 denote a turntable on which the disc D is mounted, and a clamp which secures the disc D.
A signal which is detected from the optical pickup 50 and photoelectrically converted, is input into the control unit 56 through the driving unit 54. The driving unit 54 controls a rotational speed of the spindle motor 52, amplifies the input signal and drives the optical pickup 50. The control unit 56 transmits instructions for controlling the focusing and tracking servos, which are based on the signal input from the driving unit 54, to the driving unit 54 so as to perform focusing servo and tracking servo operations
In the optical pickup actuator according to the embodiment of the present invention, negative resonance caused by leakage magnetic flux is removed such that the optical pickup actuator has stable dynamic characteristics. As such, the optical pickup can smoothly operate on any kind of optical disc, and the reproducing and recording performance of the optical disc drive apparatus, in which the optical pickup actuator is mounted, is improved. In addition, defects which may occur during a process for manufacturing an optical pickup actuator can be reduced, and jitter also can be reduced.
While this invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and equivalents thereof.
Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

An optical pickup actuator comprising:

a blade (37) on which an objective lens (39) for condensing light onto an optical disc is mounted, and on which coils are wound; and

a base (35) which includes a plurality of driving magnets (31a, 31b), which interact with current flowing through the coils, to generate force that drives the blade (37) in a predetermined direction and a shielding magnet (40), which is arranged opposite to and has the same polarity as at least one of the driving magnets (31a, 31b), to block leakage magnetic flux from the driving magnets.
The actuator of claim 1, wherein the base comprises:

a holder (34) to which the shielding magnet (40) is attached; and

a plurality of yokes (33a, b) to which the plurality of driving magnets are fixed.
The actuator of claim 1 or 2, wherein the blade comprises a plurality of guide holes (41, 43) into which the plurality of driving magnets (31a, 31b) are inserted.
The actuator of claim 1, wherein the coils comprise a focusing coil (32) wound to generate an electromagnetic force in a focusing direction and a tracking coil (36) wound to generate an electromagnetic force in a tracking direction.
The actuator of claim 2, wherein the base comprises a suspension (38), one end of which is coupled with the holder (34) and the other end of which is connected to the blade (37), to support the blade to be movable.
An optical pickup comprising:

an optical pickup actuator in accordance with any of claims 1 to 5 and further comprising an optical system which includes the objective lens (39) and a light source for radiating light through the objective lens.
An optical disc drive apparatus comprising:

an optical pickup which comprises an optical pickup actuator according to any of claims 1 to 5 and a slider at one end of which the optical pickup actuator is mounted at one end and which forms an air bearing with the optical disc to provide lift;

an optical disc rotating unit (52) which rotates the optical disc at a predetermined speed;

a driving unit (54) which drives the optical pickup and the optical disc rotating unit; and

a control unit (56) which controls focusing and tracking servos of the optical pickup.